Electrical switching apparatus including alternating current electronic trip circuit with arc fault detection circuit

ABSTRACT

An electrical switching apparatus includes a transductor circuit that senses a direct current between at least one input terminal and at least one output terminal and outputs an alternating current proportional to the direct current between the input terminal and the output terminal. The electrical switching apparatus also includes a current sensor configured to sense an alternating current component of the direct current. The electrical switching apparatus further includes an alternating current electronic trip circuit including an arc fault detection circuit configured to detect an arc fault based on the sensed alternating current component. The alternating current electronic trip circuit is also configured to control pairs of separable contacts to trip open based on the alternating current output from the transductor circuit or the detected arc fault.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority under 35U.S.C. §120 from, U.S. patent application Ser. No. 14/132,678, filedDec. 18, 2013, entitled “ELECTRICAL SWITCHING APPARATUS INCLUDINGALTERNATING CURRENT ELECTRONIC TRIP CIRCUIT WITH ARC FAULT DETECTIONCIRCUIT”, the contents of which are incorporated herein by reference.

This application is related to co-pending U.S. patent application Ser.No. 14/132,705 filed on Dec. 18, 2013, entitled “ELECTRICAL SWITCHINGAPPARATUS INCLUDING ALTERNATING CURRENT ELECTRONIC TRIP CIRCUIT WITH ARCFAULT DETECTION CIRCUIT AND POWER SUPPLY”, the entirety of which isincorporated herein by reference.

BACKGROUND

Field

The disclosed concept pertains generally to electrical switchingapparatus and, more particularly, to circuit breakers including aplurality of separable contacts.

Background Information

Circuit breakers have been used in alternating current (AC) applicationsand direct current (DC) applications. The applications for DC circuitbreakers have been very small. With the larger use of alternative energysources, such as photovoltaic applications, the DC applications areincreasing. DC molded case circuit breakers have used mechanical thermaland magnetic trip units for overload and short circuit protection, whilesome DC air circuit breakers employ electronic trip units. Magnetic tripunits instantaneously trip the circuit breaker when the current in theprotected circuit exceeds a predetermined level. However, magnetic tripunits are difficult to calibrate and are not as accurate as electronictrip units. Thermal trip units are less susceptible to nuisancetripping, but take a longer amount of time to trip the circuit breaker,and are susceptible to ambient thermal conditions causing accuracyproblems. Because of these problems thermal and magnetic trip units arenot typically used in the larger size and higher current rated circuitbreakers in AC applications, but rather, AC electronic trip units, whichuse a current transformer to sense the AC current, are used.

Without a time varying magnetic field, the AC current transformer willproduce no electromotive force with DC current, which makes the ACelectronic trip unit inoperable in DC applications. Certain DC circuitbreakers such as DC air circuit breakers have used a DC electronic tripunit in combination with a shunt to sense the DC current in theprotected circuit. The DC electronic trip unit provides enhanced controland tripping accuracy of the circuit breaker over thermal and magnetictrip units. However, DC circuit breakers which include a DC electronictrip unit are costly as compared to the high volume and readilyavailable AC electronic trip units.

Photovoltaic applications present difficulties for current DC circuitbreakers. In photovoltaic applications, the short circuit current levelcan be relatively low (e.g., less than 200% of the rated current andusually about 125% to 135% of the rated current). Due to the relativelylow short circuit current level, DC circuit breakers which use thermaland magnetic trip units are typically not desirable because it isdifficult to set the magnetic trip unit precisely at these low levelsand could cause excessive nuisance tripping and the thermal trip unitmay not offer adequate protection due to the long time it takes to tripthe circuit breaker. Additionally, thermal and magnetic trip units donot provide protection from arc faults. While a DC circuit breaker whichuses a DC electronic trip unit can offer suitable circuit protection inphotovoltaic applications, the cost of the DC circuit breaker with a DCelectronic trip unit is a concern.

There is room for improvement in electrical switching apparatus, such ascircuit breakers.

SUMMARY

These needs and others are met by embodiments of the disclosed conceptin which an electrical switching apparatus having an electronic tripcircuit includes a transductor circuit, a current sensor, and analternating current electronic trip circuit including an arc faultdetection circuit.

In accordance with one aspect of the disclosed concept, an electricalswitching apparatus comprises: a plurality of first terminals includingtwo input terminals structured to electrically connect to a directcurrent power source; a plurality of second terminals including twooutput terminals structured to electrically connect to a direct currentload; a plurality of pairs of separable contacts; an operating mechanismconfigured to open and close said separable contacts; a trip actuatorconfigured to cooperate with said operating mechanism to trip open saidseparable contacts; a plurality of conductors that electrically connecteach pair of separable contacts between one of said first terminals andone of said second terminals; a transductor circuit including first andsecond current transformers, the transductor circuit being configured tosense a direct current component of a current flowing between at leastone of the input terminals and at least one of the output terminals andto output an alternating current proportional to the direct currentcomponent; a current sensor configured to sense an alternating currentcomponent of the current flowing between at least one of the inputterminals and at least one of the output terminals; and an alternatingcurrent electronic trip circuit including an arc fault detection circuitconfigured to detect an arc fault based on the sensed alternatingcurrent component, the alternating current electronic trip circuit beingconfigured to control said trip actuator based on the alternatingcurrent output from the transductor circuit or the detected arc fault.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the disclosed concept can be gained from thefollowing description of the preferred embodiments when read inconjunction with the accompanying drawings in which:

FIG. 1 is a circuit diagram in partial block form of an electricalswitching apparatus electrically connected to an ungrounded load inaccordance with an embodiment of the disclosed concept;

FIG. 2 is a circuit diagram in partial block form of an electricalswitching apparatus electrically connected to a grounded load inaccordance with another embodiment of the disclosed concept;

FIGS. 3 and 4 are schematic diagrams of different configurations ofelectrical switching apparatus in accordance with embodiments of thedisclosed concept;

FIG. 5 is a circuit diagram in partial block form of an output interfacecircuit in accordance with embodiments of the disclosed concept;

FIGS. 6 and 7 are circuit diagrams of electrical switching apparatuswith alternating current excitation voltage sources in accordance withother embodiments of the disclosed concept; and

FIG. 8 is a circuit diagram in partial block form of an electricalswitching apparatus in accordance with another embodiment of thedisclosed concept.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As employed herein, the term “number” shall mean one or an integergreater than one (i.e., a plurality).

As employed herein, the term “electrical conductor” shall mean a wire(e.g., without limitation, solid; stranded; insulated; non-insulated), acopper conductor, an aluminum conductor, a suitable metal conductor, orother suitable material or object that permits an electric current toflow easily.

As employed herein, the statement that two or more parts are “connected”or “coupled” together shall mean that the parts are joined togethereither directly or joined through one or more intermediate parts.Further, as employed herein, the statement that two or more parts are“attached” shall mean that the parts are joined together directly.

As employed herein, the term “processor” shall mean a programmableanalog and/or digital device that can store, retrieve, and process data;a computer; a workstation; a personal computer; a controller; a digitalsignal processor; a microprocessor; a microcontroller; a microcomputer;a central processing unit; a mainframe computer; a mini-computer; aserver; a networked processor; or any suitable processing device orapparatus.

FIG. 1 is a circuit diagram of an electrical switching apparatus 1 whichcan be, for example and without limitation, a circuit breaker. Theelectrical switching apparatus 1 is electrically connected to aprotected circuit 300 (shown in phantom line drawing). The protectedcircuit 300 includes a DC power source 302 and a potentially ungroundedDC load 304. The electrical switching apparatus 1 includes one or morepairs of separable contacts 406. The electrical switching apparatus 1also includes an operating mechanism 414 that opens and closes the oneor more pairs of separable contacts 406 and a trip actuator 416 thatcooperates with the operating mechanism 414 to trip open the one or morepairs of separable contacts 406.

The electrical switching apparatus 1 further includes a transductorcircuit 100 and an AC electronic trip circuit 200. The transductorcircuit 100 is inductively coupled with the protected circuit 300. Thetransductor circuit 100 outputs an AC current to the AC electronic tripcircuit 200. The AC current output by the transductor circuit 100 isproportional to the DC current flowing in the protected circuit 300 andcan be used to determine a level of the DC current in the protectedcircuit 300.

The transductor circuit 100 includes a first current transformer 110 anda second current transformer 120. The first and second currenttransformers 110,120 include respective secondary windings 114 and 124which are inductively coupled with the protected circuit 300. The firstand second current transformers 110,120 are electrically connected inseries opposition with each other such that an electromotive forceinduced in the first current transformer 110 by the DC current in theprotected circuit 300 is opposed to an electromotive force induced inthe second current transformer 120 by the DC current in the protectedcircuit 300. By the cancellation of the electromotive forces, thisarrangement electrically neutralizes the transformer effect. Thetransductor circuit 100 can also be designed in a fashion that itmagnetically neutralizes the transformer effect.

The transductor circuit 100 also includes a power source which providesan AC voltage to the secondary windings of the current transformers 110,120. In the example shown in FIG. 1, the power source includes an ACpower source 104 and a transformer 102 to isolate the AC power source104 from the current transformers 110, 120. Arranging the currenttransformers 110, 120 in series opposition with each other and providingthe AC power source 104 causes the transductor circuit 100 to output anAC current which is proportional to the DC current in the protectedcircuit 300. It is contemplated that any suitable power source may beemployed to provide the AC voltage to the secondary windings of thecurrent transformers 110, 120. For example, in one non-limiting exampleembodiment shown in FIG. 6, the transformer 102 is omitted from thepower source and the AC power source 104 is electrically connected tothe secondary winding of the first current transformer 110. In anothernon-limiting example embodiment shown in FIG. 7, a DC/AC inverter 127 iselectrically connected to the secondary winding of the first AC currenttransformer 110 and converts a DC voltage generated by a second DC powersource 128 into the AC voltage.

Continuing to refer to the example of FIG. 1, the secondary windings 114and 124 of the current transformers 110, 120 have first ends 112 and 122and second ends 116 and 126, respectively. The first end 112 of thefirst current transformer 110 is electrically connected to the thirdtransformer 102. The second end 116 of the first current transformer 110is electrically connected to the second end 126 of the second currenttransformer 120. The first end 122 of the second current transformer 120is electrically connected to the AC electronic trip circuit 200. In theexample shown in FIG. 2, the electrical connection between the firstcurrent transformer 110 and the second transformer 120 is changed suchthat the second end 116 of the first current transformer 110 iselectrically connected to the first end 122 of the second currenttransformer 120, and the second end 126 of the second currenttransformer 120 is electrically connected to the AC electronic tripcircuit 200. However, in both of the examples of FIGS. 1 and 2, thefirst current transformer 110 and the second current transformer 120 areelectrically connected in series opposition with each other with respectto the electromotive forces induced by the DC current in the protectedcircuit 300.

The electrical switching apparatus 1 also includes a current sensor suchas the example third current transformer 130 as shown in FIGS. 1 and 2.The third current transformer 130 is inductively coupled to theprotected circuit 300. The third current transformer 130 is configuredto sense an AC component (e.g., without limitation, broadband noise) ofthe DC current flowing through the protected circuit 300 and to outputit to the AC electronic trip circuit 200. The AC component of the DCcurrent flowing through the protected circuit 300 can be used to detectan arc fault in the protected circuit 300.

The AC electronic trip circuit 200 is electrically connected to thetransductor circuit 100 and receives the AC current output by thetransductor circuit 100. The AC electronic trip circuit 200 is alsoelectrically connected to the third transformer 130 and receives thesensed AC component of the DC current flowing through the protectedcircuit 300 from the third transformer 130. The AC electronic tripcircuit 200 includes a rectifier circuit 202, an interface circuit 204,a trip threshold setting circuit 206, a processor 208, an arc faultdetection circuit 210, and an output interface circuit 212.

The rectifier circuit 202 includes a rectifier circuit input 214 and arectifier circuit output 216. The rectifier circuit input 214 iselectrically connected to the transductor circuit 100 and is structuredto receive the AC current output from the transductor circuit 100. Therectifier circuit 202 includes a full-wave rectifier and is structuredto rectify the AC current. The rectifier circuit 202 outputs therectified AC current to the rectifier circuit output 216. Although afull-wave rectifier is disclosed, it is contemplated that other suitabletypes of rectifiers may be employed such as, without limitation, ahalf-wave rectifier, with appropriate modifications to other componentsto support the change.

The interface circuit 204 includes an interface circuit input 218 and aninterface circuit output 220. The interface circuit input 218 iselectrically connected to the rectifier circuit output 216 and isstructured to receive the rectified AC current. The interface circuitinput 218 is also electrically connected to the trip threshold settingcircuit 206. The trip threshold setting circuit 206 is structured to seta an override threshold at which the processor 222 outputs a tripcontrol signal to cause the trip actuator 416 to control the operatingmechanism 414 to trip open the separable contacts 406 instantaneously.The interface circuit output 220 is electrically connected to aprocessor input 222 of the processor 208.

The processor 208 is structured to monitor the processor input 222 andto determine whether a trip condition (e.g., without limitation, an overcurrent condition) exists. The processor includes a processor output 224that is electrically connected to a first input 228 of the outputinterface circuit 212. When the processor 208 determines that a tripcondition exists, it outputs the trip control signal to the first input228 of the output interface circuit 212.

The arc fault detection circuit 210 is electrically connected to thethird transformer 130 and receives the sensed AC component of the DCcurrent flowing through the protected circuit 300 from the thirdtransformer 130. The arc fault detection circuit 210 also includes anoutput 226 electrically connected to the second input 230 of the outputinterface circuit 212. The arc fault detection circuit 210 uses thesensed AC component to detect whether an arc fault exists in theprotected circuit 300. When the arc fault detection circuit 210 detectsan arc fault in the protected circuit 300, it outputs an arc faultcontrol signal at the output 226.

The output interface circuit 212 includes the first and second inputs228,230 and an output 232. The first and second inputs 228,230 areelectrically connected to processor output 224 and arc fault detectioncircuit output 226, respectively. The output 232 is electricallyconnected to the trip actuator 416. The example output interface circuit212 is an “or” logic circuit that outputs a control signal to the tripactuator 416 to cause the trip actuator 416 to cooperate with theoperating mechanism 414 to trip open the separable contacts 406 wheneither the trip control signal is received at the first input 228 or thearc fault control signal is received at the second input 230.

Referring to FIG. 2, an example of a different configuration of theelectrical switching apparatus 1 is shown. In FIG. 2, the electricalswitching apparatus 1 has a configuration that is generally suitable fora potentially grounded load where the DC load 304 is electricallyconnected to a ground 412.

Referring to FIGS. 3 and 4, examples of different configurations of aconductive path through the electrical switching apparatus 1 are shown.FIG. 3 shows the conductive path in the electrical switching apparatus 1configured for a potentially ungrounded DC load 304 and FIG. 4 shows theconductive path in the electrical switching apparatus configured for apotentially grounded DC load 304. The conductive path includes firstterminals 402, second terminals 404, pairs of separable contacts 406,jumpers 408, and conductors 410. Two of the first terminals 402 areinput terminals which are configured to electrically connect to the DCpower source 302. Two of the second terminals 404 are output terminalswhich are structured to electrically connect to the DC load 304. Thefirst terminals 402, second terminals 404, pairs of separable contacts406, jumpers 408, and conductors 410 are electrically connected inseries to complete a power circuit between DC power source 302 and DCload 304.

The first, second, and third current transformers 110,120,130 areinductively coupled to at least one of the conductors 410. While FIGS. 3and 4 show two example placements of the first, second, and thirdcurrent transformers 110,120,130, the disclosed concept is not limitedto those example placements. The first, second, and third currenttransformers 110,120,130 may be placed at any suitable location in theprotected circuit order to inductively couple to any of the conductors410.

In the example shown in FIG. 3, the jumpers 408 are each electricallyconnected between one of the first terminals 402 and one of the secondterminals 404. In the example shown in FIG. 4, the jumpers 408 are eachelectrically connected between two of the first terminals 402 or two ofthe second terminals 404.

The change in configuration of the jumpers 408 between the examplesshown in FIGS. 3 and 4 changes the direction of the electromotive forceinduced in one of the first and second current transformers 110, 120. Assuch, when the configuration of the jumpers 408 is changed between theexample shown in FIG. 3 and the example shown in FIG. 4, the electricalconnection between the first current transformer 110 and the secondcurrent transformer 120 is also preferably changed to keep the firstcurrent transformer 110 and the second current transformer 120electrically connected in series opposition in order to neutralize thetransformer effect. The configuration of the electrical switchingapparatus 1 shown in FIG. 1 corresponds to the configuration of theconductive path shown in FIG. 3 and the configuration of the electricalswitching apparatus 1 shown in FIG. 2 corresponds to the configurationof the conductive path shown in FIG. 4. The electrical connectionbetween the first and second current transformers 110,120 changesbetween the configurations of FIGS. 1 and 2 to keep the first and secondcurrent transformers 110,120 electrically connected in series oppositionwhen the configuration of the conductive path changes between theconfigurations of FIGS. 3 and 4, respectively.

Referring to FIG. 5, example circuit components of the output interfacecircuit 212 are shown. While one configuration of circuit components forthe output interface circuit 212 is shown, it is contemplated that anysuitable configuration may be employed without departing from the scopeof the disclosed concept.

Continuing to refer to FIG. 5, the trip actuator 416 includes a tripcoil 417 which cooperates with the operating mechanism 414. The tripcoil 417 is energized by a DC voltage VDC. The DC voltage VDC may beprovided by any suitable power source (e.g., without limitation, a powersupply included in the electrical switching apparatus).

Referring to FIG. 8, an example of a different configuration of theelectrical switching apparatus 1 is shown. In the electrical switchingapparatus 1 of FIG. 8, the arc fault detection circuit output 226 iselectrically connected to a second processor input 223. In thisconfiguration of the electrical switching apparatus 1, arc faultdetection circuit 210 uses processor 208 to assist with detecting an arcfault. As such, processor 208 can output both the trip control signaland the arc fault control signal to the processor output 224. As such,output interface circuit 212 (see FIG. 1) may be omitted from theelectrical switching apparatus 1 of FIG. 8.

Although separable contacts 406 are disclosed, suitable solid stateseparable contacts can be employed. For example, the disclosedelectrical switching apparatus 1 includes a suitable circuit interruptermechanism, such as the separable contacts 406 that are opened and closedby the disclosed operating mechanism 414, although the disclosed conceptis applicable to a wide range of circuit interruption mechanisms (e.g.,without limitation, solid state switches like FET or IGBT devices;contactor contacts) and/or solid state based control/protection devices(e.g., without limitation, drives; soft-starters; DC/DC converters)and/or operating mechanisms (e.g., without limitation, electrical,electro-mechanical, or mechanical mechanisms).

While specific embodiments of the disclosed concept have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limiting as to the scope of the disclosedconcept which is to be given the full breadth of the claims appended andany and all equivalents thereof.

What is claimed is:
 1. An electrical switching apparatus structured toelectrically connect between a direct current power source and a directcurrent load, the electrical switching apparatus comprising: separablecontacts; an operating mechanism configured to open and close saidseparable contacts; a trip actuator configured to cooperate with saidoperating mechanism to trip open said separable contacts; a transductorcircuit including first and second current transformers, the transductorcircuit being configured to sense a direct current component of acurrent flowing between the direct current power source and the directcurrent load to output an alternating current proportional to the directcurrent component; and an alternating current electronic trip circuitbeing configured to control said trip actuator based on the alternatingcurrent output from the transductor circuit.
 2. The electrical switchingapparatus of claim 1, further comprising: a current sensor configured tosense an alternating current component of the current flowing betweenthe direct current power source and the direct current load, and whereinthe alternating current trip circuit includes an arc fault detectioncircuit configured to detect an arc fault based on the sensedalternating current component and to control said trip actuator based onthe detected arc fault.
 3. The electrical switching apparatus of claim2, wherein the current sensor is a third current transformer.
 4. Theelectrical switching apparatus of claim 1, wherein the alternatingcurrent trip circuit further includes: a rectifier circuit having arectifier circuit input and a rectifier circuit output, the rectifiercircuit input being electrically connected to the transductor circuit;an interface circuit having an interface circuit input and an interfacecircuit output, the interface circuit input being electrically connectedto the rectifier circuit output; and a processor having a processorinput electrically connected to the interface circuit output, theprocessor being structured to output a trip control signal based on thealternating current output from the transductor circuit.
 5. Theelectrical switching apparatus of claim 4, wherein the rectifier circuitincludes a full-wave rectifier.
 6. The electrical switching apparatus ofclaim 4, wherein the alternating current electronic trip circuit furtherincludes a trip threshold setting circuit structured to set an overridethreshold at which the processor controls the separable contacts to tripopen instantaneously.
 7. The electrical switching apparatus of claim 4,further comprising: a current sensor configured to sense an alternatingcurrent component of the current flowing between the direct currentpower source and the direct current load, wherein the alternatingcurrent trip circuit includes an arc fault detection circuit configuredto detect an arc fault based on the sensed alternating current componentand to control said trip actuator based on the detected arc fault, andwherein the arc fault detection circuit is configured to output an arcfault control signal when an arc fault is detected.
 8. The electricalswitching apparatus of claim 7, wherein the alternating currentelectronic trip circuit further includes an output interface circuithaving a first input electrically connected to the processor and asecond input electrically connected to the arc fault detection circuit;wherein the output interface circuit is configured to control said tripactuator to cooperate with said operating mechanism to trip open saidseparable contacts when the trip control signal is received at the firstinput or the arc fault control signal is received at the second input.9. The electrical switching apparatus of claim 1, wherein the firstcurrent transformer includes a first secondary winding and the secondcurrent transformer includes a second secondary winding; wherein thetransductor circuit includes an alternating current power circuitconfigured to provide an alternating voltage to the first currenttransformer and the second current transformer; and wherein the firstand second secondary windings are electrically connected inseries-opposition such that an electromotive force induced in the firstsecondary winding by the direct current component is in opposition withan electromotive force induced in the second secondary winding thedirect current component.
 10. The electrical switching apparatus ofclaim 9, wherein the alternating current power circuit includes analternating current power source and a fourth transformer; and whereinthe alternating current power source is configured to provide thealternating voltage to the first current transformer and the secondcurrent transformer via the fourth transformer.
 11. The electricalswitching apparatus of claim 9, wherein the alternating current powercircuit includes a direct current/alternating current inverter and asecond direct current power source; and wherein the directcurrent/alternating current inverter converts a direct current voltagegenerated by the second direct current power source into saidalternating voltage.
 12. The electrical switching apparatus of claim 9,wherein the first and second secondary windings each include a first endand a second end; wherein the first end of the first secondary windingis electrically connected to the third transformer; wherein the secondend of the first secondary winding is electrically connected to thesecond end of the second secondary winding; and wherein the first end ofthe second secondary winding is electrically connected to thealternating current electronic trip circuit.
 13. The electricalswitching apparatus of claim 12, wherein the direct current load ispotentially ungrounded.
 14. The electrical switching apparatus of claim9, wherein the first and second secondary windings each include a firstend and a second end; wherein the first end of the first secondarywinding is electrically connected to the third transformer; wherein thesecond end of the first secondary winding is electrically connected tothe first end of the second secondary winding; and wherein the secondend of the second secondary winding is electrically connected to thealternating current electronic trip circuit.
 15. The electricalswitching apparatus of claim 14, wherein the direct current load ispotentially grounded.
 16. The electrical switching apparatus of claim 2,wherein the alternating current electronic trip circuit furtherincludes: a rectifier circuit having a rectifier circuit input and arectifier circuit output, the rectifier circuit input being electricallyconnected to the transductor circuit; an interface circuit having aninterface circuit input and an interface circuit output, the interfacecircuit input being electrically connected to the rectifier circuitoutput; and a processor having a first processor input electricallyconnected to the interface circuit output, a second processor inputelectrically connected to the arc fault detection circuit, and aprocessor output electrically connected to the trip actuator, whereinthe arc fault detection circuit is structured to use the processor toassist with detecting the arc fault, and wherein the processor isstructured to output a trip control signal at the processor output basedon the alternating current output from the transductor circuit and tooutput an arc fault control signal at the processor output when an arcfault is detected.